The use of orthopedic bandages comprising plaster of Paris supported on a flexible material to immobilize the limb of a patient is well known in the art. Plaster of Paris has a known water sensitivity, therefore, patients wearing plaster of Paris casts must take care to avoid the rain and cannot shower. Because of this inconvenience, various improvements in the water resistance of plaster of Paris casts have been made. See, for example, U.S. Pat. Nos. 2,842,120 and 2,842,138 wherein melamine formaldehyde resin precursors have been added to plaster of Paris bandages to improve their water resistance.
Melamine formaldehyde resins have been known to cause allergic responses from the wearers of casts made from bandages of this type. Additionally, it is usually necessary to add the melamine formaldehyde precursors to the bandage in a separate step and, preferably, in an encapsulated form to preclude premature reaction. Various vinyl polymers such as polyvinyl pyrrolidone and polyvinyl acetate have also been added to improve the strength and water resistance of plaster of Paris casts (including the melamine formaldehyde resin-plaster of Paris casts noted above). See U.S. Pat. Nos. 3,671,280 and 3,649,319, respectively. Plaster of Paris casts of this type do show some improved water resistance and strength, however, further improvements in these properties would be desirable.
The addition of silicone containing materials to improve the water repellence of calcium containing masonry materials is well known in the art. In U.S. Pat. No. 2,803,561 the addition of the reaction product of a hydrolyzable, mono-hydrocarbon substituted silane and an inorganic base has been shown to improve the water repellency. There is no teaching that the addition of these silicone materials improve any property other than the water resistance of the masonry. Furthermore, there is no teaching that these materials may be used to improve the properties of plaster of Paris casts.
In U.S. Pat. No. 3,098,050, alkyl polysiloxanes which are solid materials are disclosed as improving the water repellency of masonry. These materials are said to have no effect on the setting time of masonry articles in which they are incorporated.
In U.S. Pat. No. 3,455,710 organohydrogen polysiloxane is taught as useful for waterproofing gypsum. There is no teaching of the use of these polymers for improving the water resistance of plaster of Paris orthopedic casts nor is there any teaching that the organohydrogen polysiloxane affects the cure rate of the masonry materials in any way. Furthermore, the patentee indicates that, because of the neutral or slightly acidic pH of aqueous slurries of gypsum no hydrogen liberating reaction takes place, nor would the condensation of silanol groups be expected. The patentee therefore, posits a non-reactive system.
U.S. Pat. No. 3,623,895 teaches the use of a blend of non-reactive silicones, i.e. monomethyl siloxanes and dimethyl siloxanes to waterproof masonry.
In summary, none of the above references teaches, shows or suggests the addition of reactive silicone polymers to a plaster of Paris based orthopedic bandage to improve the water resistance or the green strength of casts made therefrom.